2N VoiceBlue Next v3.1 - Manual (Page 25)

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2N TELEKOMUNIKACE a.s., www.2n.cz
®
Initiation Protocol) signalling.
Tip
In the case of separated direct connection of your SIP Proxy
and , use the G.711 codec to achieve a 2N VoiceBlue Next
®
high voice quality.
SIP Components
The following components are involved in the SIP message exchange:
UAC (User Agent Client) – the terminal device client, which initiates SIP
signalling.
UAS (User Agent Server) – the terminal device server, which responds to SIP
signalling from the UAC.
UA (User Agent) – a SIP network terminal (SIP phones, gateways to other
networks, etc.), which contains the UAC and UAS.
Proxy server – receives connection requests from the UA and transfers them to
the next Proxy server if the given station is not under it administration.
Redirect server – receives connection requests, but, instead of sending them to
the called line, sends them back to the requesting device asking for where to
route the request.
Location server – receives registration requests from the UA and updates the
terminal database accordingly.
All the server components (Proxy, Redirect, Location) are mostly on one physical
device called Proxy server, which is responsible for keeping a client database and
connection establishing, maintaining and terminating, as well as call routing.
The VoIP–GSM gateway acts as a UA in any case (has the same 2N VoiceBlue Next
®
functions as a VoIP phone), i.e. receives call set–up requirements and, on the basis of
its inner LCR table, routes calls to GSM networks.
None of the SIP–defined server components are integrated in the 2N VoiceBlue
®
gateway. Next
SIP Signalling Messages
Below is a list of messages sent via the SIP:
INVITE – connection set–up request;
ACK – INVITE confirmation by the final message addressee;
BYE – connection termination;
CANCEL – failed connection cancellation;
REGISTER – UA registration with the SIP Proxy;
OPTIONS – server capability query.
The answers to the SIP messages are numerically coded as the case is with the http
protocol. Below are the most important ones:
1XX – information messages (100 – trying, 180 – ringing, 183 – progress);
2XX – successful request completion (200 – OK);
3XX – request forwarding needed (302 – temporarily moved, 305 – use Proxy);
4XX – error (403 – forbidden, 486 – busy here);
5XX – server error (500 – Server Internal Error, 501 – not implemented);